1. Field
The present disclosure relates to a thin-film transistor substrate, and in particular relates to a thin-film transistor substrate with a self-protective conductor layer.
2. Description of the Related Art
The metal lead structure is often used in a thin-film transistor, and it may be a gate electrode, gate line, data line or source/drain electrode.
FIG. 1 shows a cross-sectional schematic representation of a typical metal lead structure 10 of prior art. The metal lead structure 10 comprises a composite metal layer 14 formed on a substrate 12, wherein the composite metal layer 14 comprises a bottom molybdenum (Mo) layer 14a, an aluminum layer 14b and a top molybdenum layer 14c. However, the conventional metal lead structure 10 has the following disadvantages.
(1) The fabrication processes of the metal lead structure 10 comprise an acid solution etching step. However, the aluminum layer 14b may be exposed by the acid solution etching step. Additionally, the exposed aluminum layer 14b may be attacked by another acid solution or base solution etchant in the following process because it is not protected.
(2) Because the thermal expansion coefficient of the aluminum layer 14b is higher than that of the bottom molybdenum layer 14a or top molybdenum layer 14c, a hillock may be formed in the aluminum layer 14b, resulting in a short-circuit problem.
(3) FIG. 2 shows a cross-sectional schematic representation of a typical via hole formed in a metal lead structure 10 of prior art. A protective layer 16 is formed on the complex metal layer 14, and a via hole 17 is formed in the protective layer 16, and a conducting layer 18 (such as indium tin oxide, ITO) is formed on the via hole 17. Because the conducting layer 18 is liable to react with the aluminum layer 14b, an unwanted insulating material 19 (such as aluminum oxide AlOx) may be formed, resulting in an electrical instability problem.
(4) When the composite metal layer 14 is used as a gate electrode and the etching process is not well controlled, the aluminum layer 14b may be exposed and the aluminum atom may diffuse into an active layer of a thin-film transistor. Thus, the thin-film transistor device exhibits poor electrical performance.
Therefore, there is a need to develop a thin-film transistor substrate with a self-protective conductor layer to solve the above-mentioned disadvantages.